The invention generally relates to a borehole communication and measurement system.
An intervention typically is performed in a subterranean or subsea well for such purposes as repairing, installing or replacing a downhole tool; actuating a downhole tool; measuring a downhole temperature or pressure; etc. The intervention typically includes the deployment of a delivery mechanism (coiled tubing, a wireline, a slickline, etc.) into the well. However, performing an intervention in a completed well may generally consume a significant amount of time and may entail certain inherent risks. Therefore, completion services that do not require intervention (called “interventionless” completion services) have become increasingly important for time and cost savings in offshore oilfield operations.
In a typical interventionless completion service, wireless signaling is used for purposes of communicating a command (for a downhole tool) from the surface of the well to a downhole receiver. More specifically, at the surface of the well, a command-encoded stimulus is produced, and this stimulus propagates downhole from the surface to a downhole receiver that decodes the command from the stimulus. The downhole receiver relays the command to the downhole tool that acts on the command to perform some desired action. Ideally, interventionless signaling should be very reliable; should consume as short a time as possible; should be applicable whether or not the well is filled with liquid up to the surface; and should be safe to the surrounding formation(s). However, conventional interventionless signaling may not satisfy all of these criteria.
For example, one type of conventional interventionless signaling involves applying a series of pressure level changes to a fluid at the surface of the well. These pressure level changes, in turn, form a command-encoded stimulus that propagates downhole to a downhole receiver. As a more specific example, an air gun may be fired in certain sequences to produce pressure changes that propagate downhole and represent a command for a downhole tool. A potential difficulty with the air gun technique is that in applications in which the well may not be filled with liquid that extends to the surface of the well, the air gun may need to produce large pressure amplitude changes. However, large pressure amplitude changes may place the formation at risk for fracturing or fluid invasion damage. Furthermore, the air gun technique may require significant knowledge of the channel properties and precise positions of echoes in order to avoid erroneous detection and/or interpretation by the downhole receiver.
Thus, there is a continuing need for a system and/or technique to address one or more of the problems that are stated above, as well as possibly address one or more problems that are not set forth above.